【单选题】What did they find out?
A.
An equatorial belt of faster moving material.
C.
A sun orbiting satellite.
【单选题】What did they find out?
A.
An equatorial belt of faster moving material.
C.
A sun orbiting satellite.
【单选题】张三与李四约定,待张三母亲去世后,张三将自己一套房屋卖给李四,双方签订了书面合同。该合同是()。